The present invention relates circuit breakers for interrupting the supply of current to a load when the current magnitude exceeds a predefined safety threshold; and particularly to circuit breakers with integral current level indicators.
Circuit breakers are commonly used to prevent excessive over current conditions from damaging electrical components or causing a fire. A wide variety of circuit breakers are available for both AC and DC applications and are connected between an electrical load and the current supply. Such devices include a mechanism for responding to an excessive current flowing through the device by opening a set of contacts, thereby disconnecting the load from the current supply.
In certain applications, it is desired that the circuit breaker provide an indication of the magnitude of current flowing to the load. Previous circuit breakers, such as the one described in U.S. Pat. No. 4,584,545, incorporated a calibrated resistive shunt in series with the set of contacts wherein current supplied to the load was conducted through the shunt. Terminals were provided so that an external voltmeter could be connected to measure a voltage across the shunt that was proportional to the current flowing to the load. Thus the shunt voltage measurement indicated the magnitude of current being conducted by the circuit breaker. These circuit breakers did not directly provide a current level indication as an external voltmeter was required.
In many circuit breakers applications, an indication of the exact amount of current being conducted is not required. Instead, a relative indication of the current magnitude with respect to the maximum rating, or trip current threshold level, is all that is necessary. Thus a precise voltmeter need not be incorporated into the circuit breaker.